Foundation for a Wind Turbine Utilizing a Slurry of Low Viscosity Grout

ABSTRACT

A self-leveling grout provides a level surface for the disposition of a wind turbine base. The self-leveling grout is placed within the foundation grout trough as an initial slurry having a viscosity at ambient temperature approximately the same as the viscosity of known grout slurries utilized in turbine foundations. After placement in the grout trough, elevated temperature is applied to the grout slurry, which lowers the viscosity of the slurry such that the slurry becomes self-leveling and the top surface assumes a nearly perfectly level surface. Additional elevated temperature is applied which initiates the curing of the grout to the required compressive strength for supporting the turbine tower.

CROSS-REFERENCE TO RELATED APPLICATIONS

U.S. Provisional Application No. 61/487,649 for this invention was filedon May 18, 2011, for which application this inventor claims domesticpriority.

BACKGROUND OF THE INVENTION

This invention relates to concrete foundations set within excavations orbore holes which are installed to support wind turbines. Moreparticularly, this invention comprises an apparatus and method forconfiguring, installing, and setting the anchor bolts for a cylindricalfoundation for a wind turbine.

U.S. Pat. Nos. 5,586,417 and 5,826,387, both by Henderson, disclose afoundation “which can be poured-on-site monolithically and is ofcylindrical construction with many post-tensioned anchor bolts whichmaintain the poured portion of the foundation under heavy compression,even during periods when the foundation may be subject to highoverturning moment.” Henderson's foundation is preferably in the shapeof a cylinder, having an outer boundary shell and an inner boundaryshell each formed of corrugated metal pipe. Between the outer boundaryshell and the inner boundary shell elongated high strength steel boltsextend vertically up through concrete from a peripheral anchor plate,called an inbed plate, located near the bottom of the cylinder. Thebolts extend upwardly from the inbed plate to a connecting plate orflange above the ground surface. The bolts extend through hollow tubesto prevent adhesion of the concrete to the bolts and thus allowing thetensioning of the bolts to the necessary pre-load. The foundationtypically uses no rebar reinforcing steel. This design uses themechanical interaction with the earth to prevent over turning instead ofthe mass of the foundation typically used by other foundations for towerstructures. FIG. 1 schematically shows an embodiment of the Hendersonfoundation.

The “hollow tubes” of the known foundation are typically elongatedplastic tubes which encase the bolts substantially through the entirevertical extent of the concrete and allow the bolts to be tensionedafter the concrete has hardened and cured, thereby post-tensioning theentire concrete foundation. Alternatively, the elongated bolts can bewrapped in plastic tape, or coated with a suitable lubrication, whichwill allow the bolts to stretch under tension over the entire operatinglength of the bolt through the vertical extent of the concrete.

Henderson further discloses the post-stressing of the concrete in greatcompression by tightening the high strength bolts to provide heavytension between a heavy top flange and the inbed plate at the bottom ofthe foundation, thereby placing the entire foundation under high unitcompression loading. The bolts are tightened so as to exceed the maximumexpected overturning force of the turbine tower on the foundation.Therefore, the entire foundation withstands various loads with theconcrete always in compression and the bolts always in static tension.

The tensioning bolts in the Henderson foundation are preferably inside-by-side pairs, the pairs extending radially from the center of thefoundation, forming an inner ring of bolts and an outer ring of bolts asshown in FIG. 2. As shown in FIG. 2, the inner ring of bolts define acircle having a slightly shorter diameter than a circle defined by anouter ring of bolts. The bolt pattern is, of course, determined by thebolt pattern on the mounting flange of the turbine tower to be installedon the foundation. A large number of bolts is typically used for thistype of foundation. Typically seventy tensioning bolts are used in theinner ring and seventy tensioning bolts in the outer ring for a total ofone hundred forty. In Henderson's foundation, the lower ends of thebolts are anchored to the inbed plate at the bottom of the foundationwhich may be constructed of several circumferentially butted and joinedsections.

The following known procedure is typically followed in constructing thecylindrical foundation. A bore hole is drilled or excavated and an outerboundary shell of corrugated metal pipe (“CMP”) is set within the hole.Bolt bundles are lowered into the borehole. The bolt bundles typicallycomprise about thirty bolts, with each bolt weighing up to two hundredpounds per bolt. Workers are lowered into the CMP lined bore hole.Working from the bottom of the bore hole, the workers lift and/orposition each individual bolt so it can be inserted into a template atthe surface, which is suspended above the bore hole by a crane having acapacity of approximately 100 tons. Once each bolt is inserted into thetemplate, a nut made up onto the threads extending above the template,such that the weight of each bolt is suspended by the template.

Once all of the bolts have been suspended from the template, the entireassembly is lifted out of the bore hole so the inbed plates may beplaced at the bottom end of the bolts. As the assembly is lowered backinto the bore hole, bands or rebar wraps are placed around thecollective bolts to hold the bolts in position during the pouring of theconcrete. FIG. 3 shows such an assembly suspended by a lifting framewhich is connected to the template. The entire assembly is then loweredback into the bore hole and an inner boundary shell of CMP is loweredinto the bore hole such that the bolts are extending upwardly through anannulus formed by the outer boundary shell and the inner boundary shell.Concrete is poured into this annulus around the upwardly extendingbolts, with the template at the top of the bolts used to form a “grouttrough” in the upper surface of the concrete. The upwardly facing endsof the bolts extend into the grout trough and, following the hardeningof the concrete, the grout trough is filled with a high strength groutupon which the tower flange is placed.

As shown in FIG. 2, flange 14 of the turbine tower 10 is set upon theanchor bolts 16. Because flange 14 must be set nearly perfectly level,shims 5 (as shown in FIG. 5) are placed in the grout trough and theshims and flange leveled through laser leveling techniques. Once theshims are leveled, the high strength grout is poured into the grouttrough and the flange 14 set down on the anchor bolts 16 and the groutallowed to set up.

Based upon the discussion above, it is clear that the integrity of thistype of foundation is dependent upon the integrity of the anchor boltsand the ability to obtain sufficient preload in the bolts. The failureof a bolt creates a stress riser on the remaining bolts, leading to thepotential failure of the entire foundation. The integrity of the steelanchor bolts can be compromised by corrosive attack. As described above,according to the current practice each anchor bolt is enclosed for mostof its length within a PVC sleeve. However, because the outside diameterof the PVC sleeve is too large for the sleeve to enter the bolt hole ofthe flange of the tower structure, the sleeve typically terminates atapproximately the top of the concrete foundation, with the bare metal ofthe anchor bolt extending above the sleeve, where the bolts extendthrough the flange and have a nut and bolt cap installed on the top sideof the flange. As with the holes of the flange of the tower base, thebolt holes in the circular template are sized to accommodate the boltdiameter, but not the diameter of the PVC sleeve, so the tops of thebolt sleeves will generally be flush with the bottom of the grout troughformed by the circular template.

In order to prevent dehydration of the grout—thus adversely impactingthe grout strength—it is a common practice to place water within thegrout trough prior to the pouring of the grout slurry to keep the groutproperly hydrated during the curing process. However, water placed inthe trough will gravitate into the ends of the PVC sleeves which areflush with the bottom of the grout trough. In the current installationpractice, a foam sleeve is typically placed around a portion of eachbare bolt extending above the bottom of the grout trough, with each foamsleeve and held in place with duct tape. The length (or height) of thefoam sleeve is sized to extend above the anticipated thickness of thegrout layer within the grout trough. In the known practice, the towerflange is set on the grout before the grout sets so that the tower basemay be leveled. It is hoped that the foam sleeve will prevent grout fromadhering to the body of the bolt, such that when the grout fully curesthe bolt may be tensioned and slide through the foam sleeve withoutdamage to the grout. However, in reality the foam sleeve is likely sodeformed by the flange of the tower base that the bolts will not slidefreely through the sleeves once the grout cures.

If a low viscosity grout slurry is used as disclosed herein with thecommonly used bolt sleeves, the flow properties of the slurry will causeit to flow into the annulus created by the PVC sleeve and the anchorbolt. Because of this problem, the use of low viscosity grouts,including epoxy grouts, has not been practical. However, the lowviscosity grouts would otherwise be preferred because of theself-leveling which may be achieved with such a material. In particular,the use of a self-leveling grout slurry would eliminate the need forleveling shims and allow the grout to be poured and adequately curebefore setting the flange onto the grout, as opposed to the currentpractice of setting and leveling the tower flange before the groutcures. The current practice requires the service of a high capacitycrane for the initial setting of the tower flange and subsequently forthe assembly of the complete turbine. However, if the tower flange canbe placed at the same time as the other turbine tower components, thecrane can be used more efficiently with less rigging up and rigging downtime at each turbine tower installation.

Once the tower has been installed and a nut and bolt cap installed onthe bolt ends extending above the tower flange, the annulus between thebolt and PVC is sealed, as illustrated in FIGS. 4 and 5. However, duringthe known installation method, the annulus between the bolt and the PVCsleeve is open thereby providing a pathway for water and other fluids toenter the annulus and be trapped between the PVC sleeve and the metallicbolt, forming a corrosion cell. Because of this opening, steps areusually taken to protect the bolt from corrosive attack and/or to sealthe sleeve-bolt annulus during installation. Unfortunately, thecurrently practiced installation procedure aggravates the situation,because, as described above, the procedure typically includes pouringwater in the grout trough to allow the grout to cure. This practiceallows to water to accumulate at the top of the PVC sleeve, andpotentially migrate into the sleeve-bolt annulus.

The initial attempt at solving the anchor bolt corrosion problem was topaint the anchor bolts along the entire length. However, this solutionis labor intensive and does not prevent liquid accumulation around theanchors. In addition, this protection method requires that the anchorsbe repainted periodically, as well as after re-tensioning the anchor ifrequired in the particular application. The currently practiced methodof protecting the anchor bolts is to seal the annulus between the top ofthe PVC sleeve and the bolt with a sealant, such as a silicon gel. Thecurrent practice also includes placing foam rings 32 or other materialaround the portion of the bolt extending above the PVC sleeve, so as toprevent adhesion of the grout to the bolt and to block the migration ofwater into the sleeve-bolt annulus. Typically, foam cylinders withlongitudinal slits are placed around the bolts, with duct tape wrappedaround each cylinder, and the cylinder pushed downwardly into contactwith the top of the PVC sleeve. However, with the large number of boltsutilized in these types of foundations, it is time consuming anddifficult to seal the top of each PVC sleeve with sealant and to installthe foam cylinders or similar devices. If hurried, the annulus may notbe adequately sealed to prevent the intrusion of water into the PVC-boltannulus. Moreover, once the tower base flange is set upon the foamcylinders, the cylinders are greatly deformed. It is non-unlikely thatwhen the anchor bolts are tensioned, the bolt does not slide through thefoam cylinder, but that the deformed foam cylinder moves within thegrout, potentially damaging the integrity of the grout.

The PVC sleeves, because of the outside diameter, displace, in totality,a significant volume of concrete in the foundation, thereby reducing theoverall compressive strength of the foundation.

SUMMARY OF THE INVENTION

The present application is directed toward methods and apparatus whichallow the utilization of a slurry of low viscosity, self-leveling grout,which results in a level surface for installing the base flange of awind turbine tower. The self-leveling grout is placed within thefoundation grout trough as an initial slurry having a viscosity atambient temperature approximately the same as the viscosity of knowngrout slurries utilized in turbine foundations. After placement in thegrout trough, elevated temperature is applied to the grout slurry, whichlowers the viscosity of the slurry such that the slurry becomesself-leveling and the top surface assumes a nearly perfectly levelsurface. Additional elevated temperature is applied which initiates thecuring of the grout to the required compressive strength for supportingthe turbine tower.

A cover structure may be utilized in combination with the low viscositygrout slurry, where the cover structure may provide the heat transferrequired to trigger the changes in the rheological properties of thegrout slurry. The cover structure also provides protection fromenvironmental conditions which might disturb the grout as is cures, suchas rain, wind, hail, etc., and potentially disrupt the top surface ofthe grout.

In an embodiment of the disclosed invention, rather than utilizing PVCsleeves which terminate at the bottom of the grout trough, the presentinvention comprises anchor bolt packages comprising a sheath or sleevewhich extends above the grout trough and, if desired, may partiallyextend inside the base flange of the wind turbine base. The sleeve maybe manufactured from polypropylene, polyethylene or other materialshaving satisfactory mechanical properties, primarily that the materialbe capable of withstanding sufficient plastic deformation to cause thematerial to conform to the shape of the threads of the anchor boltswithout failing. A tool, such as the swaging tool disclosed in theinventor's U.S. Pat. No. 7,975,519, may be used to crimp thepolypropylene sleeve along the threads of the anchor bolt.

The use of the polypropylene sleeve and the swaging of the sleeve onto aportion of the bolt provides a bolt package (i.e. a bolt/sleevecombination) which has an overall diameter less than the overalldiameter of the currently utilized bolt-PVC sleeve combination. Thisreduced diameter allows the bolt and crimped sleeve to extend throughthe bolt holes of the circular template, and into the bolt holes of thetower flange, which under the known apparatus and method, only asleeveless bolt would extend. Because the crimped sleeve extends abovethe top of the grout trough, the encased bolts will not be exposed towater placed within the grout trough, or to a low viscosity groutslurry. In addition, because the top of the crimped sleeve extends abovethe level of the grout, the crimped sleeve prevents adhesion of thegrout to the bolt, thereby allowing the bolt to move relative to thegrout.

A method of utilizing a low viscosity grout may comprise the followingsteps. Once the cement foundation has set, the foundation surface isblown free of any loose material. The components of the epoxy grout,comprising a base component and a catalyst component, are mixed togetherand pumped into the grout trough. The base component and catalyst aremixed in a sealed mixer which prevents entrainment of air bubbles in thegrout slurry. The rheological properties of the low viscosity grout aresuch that when initially catalyzed and at ambient temperature, theviscosity may be generally in the range of viscosities normally observedfor grout slurries as the slurry is pumped into the grout trough. Oncethe grout is in place, a cover structure is erected over the grouttrough, covering all of the pumped in grout slurry. The cover structurewill typically be constructed in arc length segments which are joinedtogether to form a circular structure. The cover structure has a topsurface and sides which, when joined together, cover the top of thegrout trough and enclose it on the outward side of the grout trough andthe inward side of the grout trough. The cover structure comprises heatgenerating means, such as resistance heat elements, heat lamps orburners. Utilizing the heat generating means, the temperature under thetent structure is raised to 120 degrees Fahrenheit and held at thistemperature for approximately two hours. At this elevated temperature,the grout remains ungelled and the viscosity of the grout slurrydecreases to approximately 100 centipoise. At this viscosity, the groutbecomes self-leveling such that the top surface of the grout will besufficiently close to being perfectly level. In addition, with a groutof this low viscosity for this period of time, the grout will be able topenetrate the concrete foundation. After two hours, the temperature isbrought up to 180 degrees Fahrenheit and held at the elevatedtemperature for two hours, during which time the epoxy grout gels andhardens. The heat is thereafter turned off and the grout allowed to coolfor twenty-four hours, with the protective cover, or other protectivecover, maintained over the foundation for protection. An acceptablegrout formulation is an epoxy grout manufactured by the Polyset Companyof Mechanicville, N.Y.

The advantage of the above procedure is that all of the turbinecomponents can be installed with a single crane set, thereby speeding upthe erection of the turbine while reducing the cost of equipment andmanpower. In addition, utilization of the disclosed procedure allows thefoundation bolts to be shortened by approximately eight inches each,which saves approximately $400 per installation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the foundation of Henderson following installation of theanchor bolts.

FIG. 2 shows a completed foundation, showing an inner ring of anchorbolts and an outer ring of anchor bolts with a tower base attached.

FIG. 3 shows the prior art method of placing the anchor bolts, where allof the anchor bolts are lowered into the borehole with the prior artgrout template.

FIG. 4 shows front view of a portion of a tower foundation, with thetower base flange begin lowered onto the anchor bolts.

FIG. 5 shows a portion of a grout trough, prior to the lowering of thetower base, showing the existing method of protecting the bolt-sleeveannulus with foam sleeves and utilizing shims for leveling the towerflange.

FIG. 6 shows a cross section of a portion of the base flange, grout,anchor bolt and PVC sleeve of a prior art foundation.

FIG. 7 shows a cross section of a portion of the base flange, grout,anchor bolt and sleeve according to the present invention.

FIG. 8 shows a portion of an embodiment of an anchor bolt according topresent invention showing how the sleeve is swaged around some of thethreads of the anchor bolt.

FIG. 9 shows an embodiment of a cover structure which may be used toapply heat to the grout mixture and protective the uncured grout.

FIG. 10 shows an embodiment of a cover structure utilizing a controlunit for applying heat.

FIG. 11 shows a section of the cover structure shown in FIGS. 9 and 10,showing a heating element which may be utilized.

FIG. 12A shows a sectioned side view of the cover structure shown inFIGS. 9 and 10.

FIG. 12B shows a sectioned front view of the cover structure shown inFIGS. 9 and 10.

DETAILED DESCRIPTION OF THE EMBODIMENTS Prior Art Bolt ProtectionDevices

Referring specifically to the figures, FIG. 1 depicts an embodiment of aknown foundation 100 utilized for installation of a relatively tallvertical structure, such as a wind turbine. It is to be appreciated thatwhile the disclosed method and apparatus may be utilized to obtain afoundation 100 such as that depicted in FIG. 1, the procedure forobtaining the foundation is entirely different from the known methods.Foundation 100 comprises a bore hole 120, an outer boundary shell 140and an inner boundary shell 160, each typically fashioned of corrugatedmetal pipe (“CMP”), set within the bore hole hole. An inner ring 180 ofbolts 16 and an outer ring 200 of bolts 16 are disposed within theannulus formed between the outer boundary shell 140 and the innerboundary shell 160, with the bolts 16 anchored at the lower end of thebore hole 120 to an inbed plate 220. The annulus between the outerboundary shell 140 and the inner boundary shell 160 is filled withconcrete 240 and the portion of the bore hole 120 inside the innerboundary shell 160 typically filled with loosely compacted soil 260.

FIG. 2 generally depicts the base 10 of a wind turbine set upon afoundation 12. Base 10 comprises a flange 14, by which the base isattached to foundation 12 with anchor bolts 16. As shown in FIG. 2, theanchor bolts 16 may be placed in side-by-side pairs, the pairs extendingradially from the center of the foundation 12 forming an inner ring ofbolts and an outer ring of bolts. The bolt pattern is, of course,determined by the bolt pattern on the mounting flange 14. Each anchorbolt 16 has a corresponding nut 18 which is used to secure the base 10,and to apply tension to the bolt. The exposed portion of each bolt 16 isusually protected with a bolt cap 19.

FIG. 3 depicts a bolt assembly 20 comprising a plurality of anchor bolts16 being lifted in preparation for being placed within a relatively deepexcavation prepared for construction of the foundation 12. The anchorbolts 16 typically used for wind turbines are approximately thirty feetin length, and usually have outside diameters of 1¼ inch or 1⅜ inch.Each anchor bolt 16 is partially enclosed within a “hollow tube” orsleeve 22. The sleeve is typically an elongated plastic tube fabricatedfrom polyvinyl chloride (“PVC”) which encases the bolt 16 substantiallythrough the entire vertical extent of the concrete and allows the boltto be tensioned after the concrete has hardened and cured, therebypost-tensioning the entire concrete foundation. The bolts 16 comprisingbolt assembly 20 are secured at the end by circular template 23, whichis attached to a lifting assembly 24 and lifted by crane 26.

FIG. 5 shows a close view of a portion of the grout trough 28 beforegrout has been poured or base flange 14 has been placed. Grout trough 28is formed as follows: when the concrete is poured, circular template 23,which remains attached to lifting assembly 24 and held in place by crane26, holds the bolt assembly 20 in place. Concrete is poured up aroundcircular template 23, thereby forming an inner ring groove in the top ofthe foundation 12 known as the grout trough 28. Before grout 30 isplaced in grout trough 28, a sealing member 32 comprising foam, plasticor other material, is placed around each bolt 16. Sealing member 32 istypically cylindrical in shape, having a circular opening andlongitudinal slit cut through from the outside edge to the circularopening so the sealing member may be placed around each bolt 16. Thesealing member 32 often has duct tape wrapped around it to secure it tothe bolt 16. Also shown in FIG. 5 is a leveling block 5 which is used,in combination with a number of other leveling blocks contained withinthe grout trough, to properly level the base flange 14. It is to beappreciated that the placement of leveling block 5 immediately adjacentto sealing members 32, which is not an uncommon occurrence in the priorart installations, inhibits the uniform deformation of the sealingmembers as the base flange 14 is lowered into the grout trough 28,resulting in the non-uniform deformation discussed below.

FIG. 4 depicts a portion of a prior art foundation 12 after the grouthas been poured and cured, but before flange 14 has been set upon thefoundation and nuts 18 made up onto bolts 16. As shown in FIG. 5, flange14 will be set on top of the grout 30 contained within grout trough 28.

FIG. 6 shows a cross section of a portion of the base flange 14, groutlayer 30, and sleeve 22 of a prior art anchor bolt installation for awind turbine, where sleeve 22 contains bolt 16. As shown in FIG. 6, thetop of sleeve 22 is generally flush with the bottom 34 of grout trough28. It is to be appreciated that before grout 30 is placed within grouttrough 28, the top of sleeve 22 is exposed to whatever liquids may enterthe grout trough, such as water which may be placed in the grout troughto provide for hydration of the grout. An annulus 36 is formed betweenbolt 16 and sleeve 22, which provides a potential path for water orother liquids, such as low viscosity grout, to travel along the lengthof bolt 16.

As can be seen in FIG. 6, sealing member 32 is substantially deformedonce engaged by base flange 14. It is to be appreciated that FIG. 4shows an idealized view of the deformed sealing member 32, in which thedeformation has been uniform. In actuality, it is expected that thedeformation will not be uniform because, for example, of obstructionswhich may inhibit uniform deformation such as the leveling block 5 shownin FIG. 5. It is also to be appreciated that the deformed sealing member32 displaces more volume than the non-deformed sealing member. Becauseeach bolt requires the sealing member, a typical installation may haveninety-six of the deformed sealing members 32 in the grout trough 28,thereby reducing the overall volume of grout which may be placed,resulting in a final grout pack with less strength than one having lessgrout displacement. It is also to be appreciated that once the grout 30sufficiently cures, tension will be applied to each anchor bolt 16 bythe tightening of a nut at the top of base flange 14, causing the boltto move relative to the grout. Ideally, sealing member 32 would remainstationary, allowing bolt 16 to slide through the sealing member 32.However, deformation of sealing member 32 reduces the ease with whichanchor bolt 16 will slide through the sealing member, potentiallycausing sealing member 32 to also move, potentially damaging thesurrounding grout 30.

EMBODIMENTS OF THE PRESENT INVENTION

FIG. 7 shows a cross section of a portion of the base flange 14, grout30′, and sleeve 38 which results by application of the preventinvention. In contrast to the installation shown in FIG. 6, it can beseen in FIG. 7 that the crimped sleeve 38 does not terminate at thebottom 34 of the grout trough 28 as with the prior art structure, butrather extends upwardly through and past the space in which lowviscosity grout 30′ will be placed. The crimped sleeve 38 will partiallypenetrate the bolt hole 13 of base flange 14 once the base flange isplaced over the upwardly extending bolts 16′ as shown in FIG. 7. Thisfeature prevents the top of crimped sleeve 38 from being exposed to theliquids which may be placed within grout trough 28. The use of crimpedsleeve 38 as the protective sleeve for bolt 16′ is a substantialdeparture from the present use of PVC sleeve 22, and allows the use oflow viscosity grout 30′ according to the invention described herein. Itis to be appreciated that the term “low viscosity grout” is utilized todescribe the flow characteristics of the grout slurry during a portionof the construction phase of the foundation. Once the “low viscositygrout” cures, it will have comparable compressive strength to theconventional cured grout and suitable for the service required for awind turbine foundation.

The critical distinction between the crimped sleeve 38 shown in FIG. 7from the sleeve 22 shown in FIG. 6 is that the wall thickness of thecrimped sleeve is substantially reduced, and the tolerance between theinternal diameter of the crimped sleeve and the outer diameter of thebolt threads is substantially reduced, resulting in an external diameterof the crimped sleeve which is smaller than possible with thethicker-walled PVC sleeves. This reduced diameter allows the crimpedsleeves 38 to extend into the bolt holes 13 of the base flange 14. Forexample, a crimped sleeve comprising polypropylene sleeves has a closertolerance than the available PVC, such that the crimped sleeves may havea clearance of 20 thousands of an inch between the internal diameter ofthe crimped sleeve and the outer diameter of the anchor bolt threads.

As shown in FIG. 7, this smaller outside diameter of the crimped sleeve38 allows a portion of the sleeve to be disposed within the holes 13 inthe base flange 14. In contrast, the known installations utilize PVCsleeves 22 which terminate at the bottom 34 of the grout trough 28 asshown in FIG. 5, rather than extending into the base flange 14 of thewind turbine because the external diameters of commonly available PVCsleeves 22 are too large to be inserted within the holes of the flange.

As shown in FIG. 7, and in greater detail in FIG. 8, the top of thecrimped sleeve 38 is “swaged” such that a portion of the sleeve conformsto the threads of the anchor bolt 16′. The swaging serves severalpurposes. First, the swaging retains the crimped sleeve 38 on the anchorbolt 16′ such that nuts are not required to retain the sleeve on theanchor bolt during transportation. This characteristic allows the anchorbolts 16′ to be shipped without nuts, which reduces manpower requiredfor placing the nuts on the bolts for transportation and removing of thebolts upon arrival.

The swaging further inhibits the flow of liquids into the annulusbetween the crimped sleeve 38 and the anchor bolt 16′, although it is tobe appreciated that the exposure of the sleeve end to liquid is reducedor eliminated, because of the capability of placing the top of thecrimped sleeve 38 above the grout trough 28 and partially within thebase flange 14 once the tower base is installed. It has been found thatswaging approximately two inches of the top of the crimped sleeve 38forms a sufficient length of “crimps” 17 (i.e., portions of the sleeve38 which conform to the shape of individual threads 21) to form aninterference fit which adequately inhibits liquid penetration into thesleeve-bolt annulus.

It has been found that sleeves 38 comprising polypropylene, or similarmaterials, have the desired mechanical properties for swaging the sleevematerial such that it conforms to the shape of the threads. Themechanical properties of the polypropylene are such that the materialhas a “memory” and retains the crimps 17 once the swaging operation hasbeen completed. U.S. Pat. No. 7,975,519 discloses a swaging tool whichmay be utilized to swage the polypropylene sleeve 38. It is also to beappreciated that when the anchor bolts 16′ are tensioned by thetightening of the nuts 18, the mechanical properties of the sleevematerial are such that upon tensioning of the anchor bolt 16′, thematerial will plastically deform and the crimps 17 will relax and allowrelative movement of the anchor bolt with little resistance such thatthe anchor bolts 16′ may be properly preloaded.

FIGS. 9 through 12 show a cover structure 50 which may be utilized toapply heat to the slurry of the low viscosity grout 30′. FIGS. 9 through12 show a portion of the foundation after the anchor bolts 16′ havealready been set within cement 240 and a slurry of the low viscositygrout 30′ is introduced into the grout trough 28. For simplicity,polypropylene sleeves 38 are not shown in these figures, but it shouldbe understood that the anchor bolts 16′ are contained within thepolypropylene sleeves as described above.

The cover structure may comprise a plurality of individual sections 52.The cover structure 50 comprises a plurality of apertures 54 which aresized to fit over the upwardly facing ends of anchor bolts 16′ The coverstructure 50 may further comprise a fan 56 which evenly disperses heatthroughout the cover structure. FIG. 10 shows a cover structure 50placed over the grout trough 28 after the slurry of low viscosity grout30′ has been introduced into the trough.

FIG. 11 shows a bottom view of an individual section 52 of the coverstructure 50, with cover plate 62 removed. The individual sections 52may comprise heater elements 58. Heater elements 58 may beresistance-type heating elements which receive current from a controller60. Controller 60 may be controlled with a programmable controller toprovide current at particular magnitudes for pre-selected times toprovide a desired temperature sequence for controlling the rheologicalproperties of the low viscosity grout 30′. The cover structure mayfurther comprise a thermostat (not shown) so that the controller 60 maymake temperature corrections to adjust the temperature within the coverstructure 50 as necessary to achieve the desired rheological properties.

A method of utilizing a low viscosity grout may comprise the followingsteps. Once the cement foundation has set, with a grout trough 28 formedin the top surface of the concrete, the foundation surface is blown freeof any loose material. The components of the low viscosity grout 30′,comprising an epoxy base component and a catalyst component, are mixedtogether in a slurry and pumped into the grout trough. The epoxy basecomponent and catalyst are mixed in a sealed mixer which preventsentrainment of air bubbles in the grout slurry. The rheologicalproperties of the low viscosity grout are such that when initiallycatalyzed and at ambient temperature, the viscosity may be generally inthe range of viscosities normally observed for grout slurries as theslurry is pumped into the grout trough.

Once the low viscosity grout 30′ is in place, a cover structure 50 iserected over the grout trough 28, covering all of the pumped in grout.The cover structure 50 will typically been constructed in arc lengthsections 52 which are joined together to form a continuous structure,such the circular structure shown in the figures. The cover structure 50has a top surface and sides which, when joined together, cover the topof the grout trough 28 and enclose it on the outward side of the grouttrough and the inward side of the grout trough. The cover structurecomprises heat generating means, such as resistive heat elements 58,heat lamps or burners.

With one embodiment of low viscosity grout 30′, the heat generatingmeans is utilized to raise the temperature under the cover structure toapproximately 120 degrees Fahrenheit. This temperature is heldapproximately constant for approximately two hours. At this elevatedtemperature, the slurry of low viscosity grout 30′ remains ungelled andthe viscosity of the grout slurry decreases to approximately 100centipoise. At this viscosity, the low viscosity grout slurry 30′becomes self-leveling such that the top surface of the grout slurry willbe sufficiently close to being perfectly level to provide a suitablelanding surface for the tower flange 14. After about two hours, thetemperature is brought up to approximately 180 degrees Fahrenheit andheld at the elevated temperature for two hours, during which time thegrout gels and hardens. The heat is thereafter turned off and the groutallowed to cool for twenty-four hours, with the cover structure 50remaining in place over the foundation for protection.

Other grout formulations might be utilized so long as the groutpossesses the rheological properties described above. In other words:(1) an initial slurry viscosity at ambient temperature which isapproximately the same as the viscosity of known grout slurries utilizedin turbine foundations; (2) a lower viscosity of triggered byapplication of an initial elevated temperature or a chemical catalyst atwhich viscosity the grout slurry is self-leveling, the top surfaceassuming a nearly perfectly level position; and (3) a temperature“trigger” or catalyst which initiates the curing of the grout to therequired compressive strength for supporting the turbine tower.

When it comes time for erection of the tower base 10, the coverstructure 50 is removed from the foundation. Foundation nuts 18 are madeup on both the inside ring 180 of anchor bolts 16′ and outside ring 200of anchor bolts, and equipment for placing the anchor bolts at thedesired tension is put into position. The tower base 10 is positioned onthe anchor bolts 16′ with several nuts 18 installed to preventbounce-off. At this point, a half-inch bead of fast setting epoxy may beplaced on the outside peripheral edge of the grout trough, whilesimultaneously a half-inch bead of fast setting epoxy is placed on theinside peripheral edge of the grout trough, to form an outer ring andinner ring of bedding epoxy. This bedding epoxy is a very fast set andcure catalyzed epoxy with a five minute open time and 5,000 plus psicompressive strength in one hour. While not an essential element of thepresent invention, the bedding epoxy does allow the correction of anydeviation in the tower flange 14 to insure 100 percent tangency to thecured grout, because tower base flanges are held to less than 0.020deviation in the flange. The tower base 10 is set down on the uncuredbedding epoxy and nuts 18 are installed and run down on the anchor bolts16′. After the midsection of the tower is installed, the bedding epoxyis cured to at least the compressive strength of the foundationconcrete. The anchor bolts 16′ are thereafter tensioned to the desiredamount before the installation of the upper tower section.

While the above is a description of various embodiments of the presentinvention, further modifications may be employed without departing fromthe spirit and scope of the present invention. Thus the scope of theinvention should not be limited according to these factors, butaccording to the following appended claims.

1. A method for using low-viscosity grout in the installation of a windturbine foundation, the method comprising the steps of: providing aplurality of anchor bolts within a generally vertical excavation;cementing the anchor bolts within the excavation wherein a top surfaceof the cement comprises a grout trough; introducing a slurry oflow-viscosity grout into the grout trough, the slurry of low-viscositygrout comprising the rheological properties of having a first viscosityat ambient temperature and a second viscosity at a first elevatedtemperature, wherein the first viscosity is higher than the secondviscosity, and the grout self-levels to a level surface at the firstelevated temperature; allowing the low-viscosity grout to cure to anacceptable compressive strength; and securing a base flange to theanchor bolts.
 2. The method according to claim 1 wherein each of saidanchor bolts is disposed within a sleeve extending substantially alongthe length of the anchor bolt, the method further comprising the step ofobstructing an opening between an interior wall of the sleeve and asurface of the anchor bolt such that the low-viscosity grout cannotenter into a space between the interior wall of the sleeve and thesurface of the anchor bolt.
 3. The method according to claim 2 whereinthe opening between an interior wall of the sleeve and a surface of theanchor bolt is obstructed by providing a swaged upper end of said sleeveconforming substantially to a surface of said anchor bolt.
 4. The methodaccording to claim 1 wherein the slurry of low viscosity grout comprisesan epoxy, and further comprising the steps of mixing a base component ofsaid grout and a catalyst component of said grout prior to introducingthe slurry of low viscosity grout into the trough.
 5. The methodaccording to claim 1 further comprising the step of heating the slurryof the low viscosity grout further, such that the slurry hardens to agrout having an acceptable compressive strength to support the weight ofthe base flange in a level position.
 6. The method according to claim 5further comprising the step of allowing the grout to cool prior tosecuring the base flange.
 7. The method according to claim 1 whereinheat is applied to the slurry of low-viscosity grout by a coverstructure comprising heating elements.
 8. The method of claim 7 whereinthe cover structure comprises means for evenly distributing heat aboutthe slurry of low viscosity grout.
 9. The method of claim 7 wherein thecover structure comprises a plurality of arc length sections.
 10. Afoundation for supporting a wind turbine comprising: a plurality ofanchor bolts disposed within a vertical excavation; a cement disposedwithin the vertical excavation such that a substantial portion of alength of each of said plurality of anchor bolts is embedded within thecement, the cement having an upper surface defining a trough; and agrout disposed within said trough, the grout initially introduced intothe trough as a slurry having the rheological properties of having afirst viscosity at ambient temperature and a second viscosity at a firstelevated temperature, wherein the first viscosity is higher than thesecond viscosity, and the grout slurry is self-leveling to a levelsurface at the first elevated temperature.
 11. The foundation accordingto claim 10 further comprising a sleeve extending substantially alongthe length of an anchor bolt, the sleeve preventing contact between theanchor bolt and the cement, the sleeve comprising a swaged upper endsuch that the upper end of the sleeve conforms substantially to asurface of the anchor bolt.
 12. The foundation according to claim 10wherein the trough is an annular trough.
 13. A method of constructing afoundation for a wind turbine tower, comprising the following steps:providing a plurality of anchor bolt packages within a generallyvertical excavation, wherein each anchor bolt package comprises ananchor bolt and a polypropylene sheath extending along a substantialportion of the exterior of the anchor bolt; cementing the anchor boltswithin the excavation wherein a top surface of the cement comprises agrout trough with upwardly extending ends of the anchor bolt packagesextending above the grout trough; introducing a low-viscosity groutslurry into the grout trough, the low-viscosity grout slurry comprisingthe rheological properties of having a first viscosity at ambienttemperature and a second viscosity at a first elevated temperature,wherein the first viscosity is higher than the second viscosity, and thegrout is self-leveling to a level surface at the first elevatedtemperature; allowing the low-viscosity grout slurry to cure to anacceptable compressive strength, the grout slurry curing to a hardenedgrout having a perfectly level top surface; lowering a base flange ontothe level top surface of the hardended grout; and securing a base flangeto the upwardly extending ends of the anchor bolt packages.
 14. Themethod according to claim 13 wherein heat is applied to the slurry oflow-viscosity grout by a cover structure comprising heating elements.15. The method of claim 14 wherein the cover structure comprises meansfor evenly distributing heat about the slurry of low viscosity grout.16. The method of claim 14 wherein the cover structure comprises aplurality of arc length sections.
 17. The method of claim 14 wherein thecover structure comprises control means for adjusting the temperaturewithin the cover structure.